[EE] RS232 protection

Hi all,

I'm reading data from a very expensive device in a vehicle over RS232, 
using a MAX3232 chip.
Just reading, so only one data line and +12V/Gnd coming from the 
vehicle's power outlet.
Out of an abundance of caution, I would like to do anything extra I can 
to help protect the expensive device from anything that could go wrong 
with my add-on. Even shorted wires, etc.
I did find some (expensive) chips that help with this, specifically ESD, 
but wondering what other in-between things I can do to just help isolate 
my device from the one in the vehicle.
Suggestions welcome.

Cheers,
-Neil.